Single crystal material auxiliary melting apparatus and single crystal material melting method

ABSTRACT

The present invention aims to improve thermal efficiency and to reduce melting time when a raw material in an auxiliary crucible is heated and melted by induction heating method. When an initial raw material  30   a  is at low temperature and its conductivity is relatively low, a conductive carbon cylinder  2  is arranged at such a height as to cover the entire side wall of the auxiliary crucible  1 , and when high frequency current is applied on a high frequency coil  3 , secondary induction current is generated on the carbon cylinder  2 . Then, Joule heat is generated on the carbon cylinder  2  by the secondary induction current, and heat of the carbon cylinder  2  is transmitted to the raw material inside via the auxiliary crucible  1 . Thus, the raw material is heated, and melting is started. When the raw material is melted, an insulating ceramic base  4  is arranged at such a position as to cover the entire side wall of the auxiliary crucible  1 . Because conductivity of the raw material is gradually increased, secondary induction current is generated in the melt  30   b , and Joule heat is generated in the melt  30   b  itself by the secondary induction current.

TECHNICAL FIELD

The present invention relates to a single crystal material auxiliarymelting apparatus and a single crystal material melting method forheating and melting a single crystal material in an auxiliary crucibleand for supplying the melt to a main crucible in a single crystalpulling apparatus for manufacturing dislocation-free single crystal ofsilicon (Si) by Czochralski pulling method.

BACKGROUND ART

In general, in a single crystal manufacturing apparatus based onCzochralski pulling method, the pressure in a highly pressure-resistantairtight chamber is reduced to about 10 torr and fresh argon (Ar) gas issupplied into it, and polycrystal in a quartz crucible installed in thelower portion of the chamber is heated and melted. A seed crystal isimmersed from above into the surface of the melt. Then, the seed crystaland quartz crucible are rotated and moved up and down, and the seedcrystal is pulled so that a single crystal (the so-called ingot) isgrown, which comprises an upper cone portion in conical shape with itsupper end protruding under the seed crystal, a body portion incylindrical shape, and a lower cone portion in conical shape with itslower end protruding.

As a conventional method to melt the raw material in an apparatus asdescribed above, a method for supplying raw material to supplement thedecrease of the melt in a crucible (hereinafter referred as “maincrucible”) for pulling up single crystal has been proposed. For example,JP-A-55-130894 discloses a method for melting raw material in anauxiliary crucible communicated with a main crucible and foradditionally supplying the melt from the auxiliary crucible to the maincrucible via a communicating pipe. Also, JP-A-56-164097 describes amethod for supplying and melting solid raw material in an auxiliarycrucible in a pulling apparatus from outside the pulling apparatus andfor additionally supplying the melt from the auxiliary crucible to themain crucible.

In the past, as the methods for heating and melting raw material ofsingle crystal in an auxiliary crucible, resistance heating method andinduction heating method have been known. In the resistant heatingmethod, a resistance heater is disposed around the auxiliary crucible,and heat is generated by applying DC voltage on the heater, and the rawmaterial inside is heated via the auxiliary crucible. In the inductionheating method, a coil is installed around the auxiliary crucible, andby applying AC voltage on the heater, secondary induction current isgenerated on the raw material in the auxiliary crucible. Then, Jouleheat is generated on the raw material by the secondary inductioncurrent, and the raw material is melted.

In the resistance heating method as described above, however, the heatgenerated by the heater is indirectly transmitted to the raw materialinside via the auxiliary crucible, and thermal efficiency is not veryhigh. As a result, melting time becomes longer, and the auxiliarycrucible which is made of quartz and is easily deteriorated at hightemperature must be heated to unnecessarily high temperature. Further,the auxiliary crucible must be rotated to stir up the raw material, andthis requires a system with more complicated structure.

Also, in a conventional example based on the induction heating method asdescribed above, conductivity of silicon is low at low temperature andhigh at high temperature. This leads to the problem that thermalefficiency is low at the initial heating. Accordingly, when this methodis used, induction heating must be started after a part of raw materialis melted at the initial heating and supplied into the auxiliarycrucible in order to reduce the melting time.

DISCLOSURE OF THE INVENTION

To overcome the above problems, it is an object of the present inventionto provide a single crystal material auxiliary melting apparatus and asingle crystal material melting method, by which it is possible toimprove thermal efficiency and to reduce melting time when the rawmaterial in the auxiliary crucible is heated and melted by inductionheating method.

According to a first invention of the present application, when the rawmaterial is at low temperature and its conductivity is relatively low,secondary induction current is generated on a susceptor and heat of thesusceptor is transmitted to the raw material in the auxiliary crucible,and when the raw material is at high temperature and its conductivity isrelatively high, the susceptor is moved aside and secondary inductioncurrent is generated on the raw material in the auxiliary crucible, andheat is generated in the raw material itself.

Specifically, the first invention of the present application provides asingle crystal material auxiliary melting apparatus for heating andmelting a single crystal raw material in an auxiliary crucible and forsupplying the melt into a main crucible, the apparatus comprising:

a conductive susceptor arranged around the auxiliary crucible so that itcan be moved in vertical direction;

a coil wound around the susceptor and with high frequency currentapplied thereon; and

means for moving the susceptor in such manner that heating of the rawmaterial in the auxiliary crucible is started by arranging the susceptorat a high position on the auxiliary crucible and by heating thesusceptor with secondary induction current the susceptor is moved asidefrom the position on the auxiliary crucible after melting of the rawmaterial has been started, and the raw material in the auxiliarycrucible is heated by secondary induction current.

The first invention of the present application also provides a singlecrystal material melting method in a single crystal material auxiliarymelting apparatus, which comprises an auxiliary crucible for heating andmelting a single crystal raw material and for supplying the melt into amain crucible, a conductive susceptor arranged around the auxiliarycrucible so that the susceptor can be moved in vertical direction, and acoil wound around the susceptor and with high frequency current appliedthereon, whereby the method comprises the steps of:

starting to heat the raw material in the auxiliary crucible by arrangingthe susceptor at a high position on the auxiliary crucible and bygenerating heat on the susceptor with secondary induction current; and

moving the susceptor aside from the high position on the auxiliarycrucible after melting of the raw material has been started, andgenerating heat on the raw material in the auxiliary crucible bysecondary induction current.

In a second invention of the present application, in order to attain theabove object, a mass of the raw material is placed on an opening of apipe to block it and a susceptor is arranged at a position no to heatthe mass of the raw material and heating is started, and after themelting of the raw material has been started, the susceptor is arrangedat a position to heat the mass of the raw material and the raw materialabove it, and heat is generated on both the susceptor and the rawmaterial by secondary induction current.

Specifically, the second invention of the present application provides asingle crystal material auxiliary melting apparatus for heating andmelting a single crystal raw material in an auxiliary crucible and forsupplying the melt into a main crucible, the apparatus comprising:

a conductive susceptor arranged around the auxiliary crucible so that itcan be moved in vertical direction;

a coil wound around the susceptor and with high frequency currentapplied thereon;

a pipe having an opening to supply the melt from the auxiliary crucibleinto the main crucible and formed on the bottom wall of the auxiliarycrucible;

means for starting to heat the raw material in the auxiliary crucible bygenerating heat on the susceptor with secondary induction current and byarranging the susceptor at such a height that a mass of the raw materialis not heated and the raw material above the mass is heated, while themass of the raw material blocks opening of the pipe; and

means for generating heat on both the susceptor and the raw materialwith secondary induction current and by arranging the susceptor at sucha height that the mass of the raw material and the raw material abovethe mass are heated after melting of the raw material has been started.

Also, the second invention provides a single crystal material meltingmethod in a single crystal material auxiliary melting apparatus, whichcomprises an auxiliary crucible for heating and melting a single crystalraw material and for supplying the melt into a main crucible, aconductive susceptor arranged around the auxiliary crucible in suchmanner that the susceptor can be moved in vertical direction, a coilwound around the susceptor and with high frequency current appliedthereon, and a pipe with an opening for supplying the melt from theauxiliary crucible into the main crucible, the pipe being formed onbottom wall of the auxiliary crucible, whereby the method comprises thesteps of:

arranging the susceptor at such a height as not to heat the raw materialmass but to heat the raw material above the mass with the raw materialmass placed on the opening of the pipe, and starting to heat the rawmaterial in the auxiliary crucible by generating heat on the susceptordue to the secondary induction current; and

arranging the susceptor at such a height to heat the raw material massand the raw material above the mass after melting of the raw materialhas been started, and generating heat on both of the susceptor and theraw material due to secondary induction current.

Further, according to a third invention of the present application, inorder to attain the above object, when the raw material is at lowtemperature and its conductivity is relatively low, secondary inductioncurrent is generated on the susceptor and heat of the susceptor istransmitted to the raw material in the auxiliary crucible, and when theraw material is at high temperature and its conductivity is relativelyhigh, secondary induction current is generated in both the susceptor andthe raw material inside the auxiliary crucible, and heat of thesusceptor is transmitted to the raw material in the auxiliary crucibleand heat is generated in the raw material itself. Also, by switchingover the frequency of the high frequency current to be applied duringthe melting process, the melting time can be reduced further.

The third invention of the present application provides a single crystalmaterial auxiliary melting apparatus for heating and melting a singlecrystal raw material in an auxiliary crucible and for supplying the meltinto a main crucible, said apparatus comprising:

a conductive susceptor for supporting the auxiliary crucible; and

a coil wound around the susceptor and with high frequency currentapplied thereon, whereby:

thickness of the susceptor and frequency applied on the coil areselected in such manner than the thickness of the susceptor will bethinner than penetration depth of the secondary induction current.

Also, the third invention of the present application provides a singlecrystal material auxiliary melting apparatus for heating and melting asingle crystal raw material in an auxiliary crucible and for supplyingthe melt into a main crucible, the apparatus comprising:

a conductive susceptor for supporting the auxiliary crucible; and

a coil wound around the susceptor and with high frequency currentapplied thereon, whereby:

heating in the auxiliary crucible is started by applying electriccurrent with relatively high first frequency on the coil and electriccurrent with relative low second frequency is applied after melting ofthe raw material has been started.

Further, the third invention of the present application provides asingle crystal material melting method in a single crystal materialauxiliary melting apparatus for heating and melting a single crystal rawmaterial in an auxiliary crucible and for supplying the melt into a maincrucible, the apparatus comprising a conductive susceptor for supportingthe auxiliary crucible, and a coil wound around the susceptor and withhigh frequency current applied thereon, whereby the method comprises thesteps of:

applying electric current with relatively high first frequency on thecoil and starting to heat the material in the auxiliary crucible; and

applying electric current of relatively low second frequency aftermelting of the raw material has been started.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention as described abovewill become more apparent by the detailed description given below inconnection with the attached drawings:

FIG. 1 is a schematical drawing to show a single crystal pullingapparatus, to which a first embodiment of a single crystal materialauxiliary melting apparatus of the present invention is applied;

FIG. 2 is a drawing to show an auxiliary melting process of an auxiliarymelting apparatus shown in FIG. 1;

FIG. 3 is a drawing to show an auxiliary melting process of an auxiliarymelting apparatus shown in FIG. 1;

FIG. 4 is a drawing to show an auxiliary melting process of an auxiliarymelting apparatus shown in FIG. 1;

FIG. 5 is a drawing to show an auxiliary melting process of an auxiliarymelting apparatus of a second embodiment of the present invention;

FIG. 6 is a drawing to show an auxiliary melting process of an auxiliarymelting apparatus of a second embodiment of the present invention;

FIG. 7 is a drawing to show an auxiliary melting process of an auxiliarymelting apparatus of a second embodiment of the present invention; and

FIGS. 8(a), 8(b) and 8(c) each represents an auxiliary melting processof an auxiliary melting apparatus of a third embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, description will be given on embodiments of thepresent invention referring to the attached drawings. FIG. 1 is aschematical drawing of a single crystal pulling apparatus, to which afirst embodiment of a single crystal material auxiliary meltingapparatus of the present invention is applied. FIG. 2 to FIG. 4 eachrepresents a drawing to explain an auxiliary melting process of theauxiliary melting apparatus of FIG. 1.

In a single crystal pulling apparatus 10 shown in FIG. 1, a heater ofcylindrical shape (not shown) is arranged around a main crucible 11 madeof quartz, and a heat insulating material 13 of cylindrical shape isdisposed around the heater. These component members 11 and 13 arearranged within a lower chamber 14. Although not shown in the figure,the main crucible 11 is supported by a carbon crucible, and the maincrucible 11 and the carbon crucible are rotatably supported around ashaft so that these crucibles can be moved up and down in verticaldirection. Also, an upper chamber 15 is disposed above the lower chamber14, and a cable for pulling up the single crystal is suspended from theupper chamber 15 so that it can be moved in vertical direction and canbe rotated around a shaft.

Also, an auxiliary chamber 17 is arranged above the lower chamber 14,and an auxiliary melting apparatus 20 as shown in detail in FIGS. 2 to 4is placed in the auxiliary chamber 17 in order to supply the melt intothe main crucible 11. Further, above the auxiliary melting apparatus 20,a feeder 21 for supplying solid grain-like material, i.e. raw materialfor the single crystal, is arranged. The inner space of the lowerchamber 14 is communicated with the inner spaces of the upper chamber 15and the auxiliary chamber 17, and these spaces are maintained at lowpressure and are filled with inert gas such as argon.

Now, detailed description will be given on the auxiliary meltingapparatus 20 referring to FIG. 2 to FIG. 4. At the center of theauxiliary crucible 1 made of quartz, a pipe 1 a for supplying the meltfrom the auxiliary crucible 1 into the main crucible 11 by overflow isinstalled so that an opening at the upper end of the pipe 1 a isprotruded at a position about ½ of the height of the auxiliary crucible1. Around the auxiliary crucible 1, a carbon cylinder (carbon crucible)2, serving as a conductive susceptor, is arranged in such manner that itcan be moved up and down in vertical direction.

A high frequency coil 3 is disposed around the carbon cylinder 2, andthe lower end of the carbon cylinder 2 is supported by an insulatingceramic base 4 in cylindrical shape made of a material such as Si₃N₄.The carbon cylinder 2 is assembled with the ceramic base 4 so that thesecan be integrally moved in vertical direction, and the high frequencycoil 3 is fixed at such a position as to match the auxiliary crucible 1.Here, secondary induction current is likely to concentrate on thesurface of a conductive member, and this tendency is more remarkable athigher frequency. In this respect, thickness of the carbon cylinder 2and frequency applied on the high frequency coil 3 are selected in suchmanner that the thickness of the carbon cylinder 2 will be thinner thanpenetration depth of the secondary induction current.

FIG. 2 shows a condition prior to the melting process, FIG. 3 shows acondition during melting process, and FIG. 4 shows a condition whenmelting process is completed. When a raw material 30 is not yet melted,i.e. when an initial raw material 30 a is at low temperature and itsconductivity is relatively low, the conductive carbon cylinder 2 isarranged at such a height that it covers the entire side wall of theauxiliary crucible 1. If high frequency current is applied on the highfrequency coil 3 under this condition, secondary induction current isgenerated on the carbon cylinder 2, and Joule heat is generated on thecarbon cylinder 2 due to the secondary induction current. In this case,the secondary induction current is not generated almost at all becausethe conductivity of the initial raw material 30 a is lower than that ofhigh temperature. Therefore, the heat of the carbon cylinder 2 istransmitted to the raw material inside via the auxiliary crucible 1. Asa result, the raw material is heated, and melting is started as shown inFIG. 3.

When the raw material is in melting process (30 b in the figure) asshown in FIG. 3, the carbon cylinder 2 and the ceramic base 4 are bothmoved upward and the insulating ceramic base 4 is arranged at such aheight that the entire side wall of the auxiliary crucible 1 is covered.In this case, conductivity of the raw material is gradually increasedand secondary induction current is generated in the melt 30 b, and Jouleheat is generated on the melt 30 b itself by the secondary inductioncurrent.

Next, as shown in FIG. 4, melting process proceeds. Conductivity of theraw material reaches the maximum value, and the secondary inductioncurrent inside the raw material also reaches the maximum value. Bymagnetic field generated by the high frequency coil 3, the melt 30 b ismoved by convection, and self-stirring occurs. Under this condition,grain-like raw material 30 is added into the auxiliary crucible 1 viathe feeder 21. Then, the carbon cylinder 2 and the ceramic base 4 areboth moved downward, and the conductive carbon cylinder 2 covers upperhalf of the side wall of the auxiliary crucible 1, and the insulatingceramic base 4 is positioned at such a height to cover lower half of theside wall of the auxiliary crucible 1. As a result, the melt 30 b in theauxiliary crucible 1 overflows into the pipe 1 a and it is supplied tothe main crucible 11 via the pipe 1 a. Because heat is generated on thecarbon cylinder 2, the added grain-like raw material 30 is heated as theresult of heat transfer, and melting rate is increased. In this case,heat is generated on the melt 30 b in the auxiliary crucible 1 by thesecondary induction current.

Next, description will be given on a second embodiment of the inventionreferring to FIG. 5. In this embodiment, a pipe 1 b for supplying themelt from the auxiliary crucible 1 into the main crucible 11 is notprotruded upward from bottom wall of the auxiliary crucible 1, and anopening is formed on the bottom wall of the auxiliary crucible 1. Theother arrangement is the same as in the first embodiment.

FIG. 5 shows a condition prior to the melting, FIG. 6 shows a conditionduring melting process, and FIG. 7 shows a condition at the completionof melting process. First, when the raw material 30 is still beforebeing melted as shown in FIG. 5, i.e. when the initial raw material 30 ais at low temperature and its conductivity is relatively low, a mass 30c of the initial raw material 30 a is disposed at the opening of thepipe 1 b as if it serves as a stopper. In order to prevent the mass 30 cserving as stopper from being melted, the conductive carbon cylinder 2covers about ⅔ of the upper portion of the side wall of the auxiliarycrucible 1, and the insulating ceramic base 4 is positioned at such aheight as to cover about ⅓ of the upper portion of the side wall of theauxiliary crucible 1. When high frequency current is applied on the highfrequency coil 3 under this condition, secondary induction current isgenerated on the carbon cylinder 2, and Joule heat is generated on thecarbon cylinder by the secondary induction current. Then, the heat ofthe carbon cylinder 2 is transmitted to about ⅔ of the upper portion ofthe raw material inside via the auxiliary crucible 1. As a result, theraw material is heated, and melting is started as shown in FIG. 6.

Next, when the raw material is in melting process (30 b in the figure)as shown in FIG. 6, the carbon cylinder 2 and the ceramic base 4 areboth moved downward, and the conductive carbon cylinder 2 is positionedat such a height as to cover the entire side wall of the auxiliarycrucible 1. In this case, conductivity of the raw material is graduallyincreased and secondary induction current is generated on both thecarbon cylinder 2 and the melt 30 b, and Joule heat is generated on themelt 30 b itself because of the secondary induction current.

Next, as shown in FIG. 7, melting process proceeds, and conductivity ofthe raw material reaches the maximum value, and the secondary inductioncurrent inside the raw material also reaches the maximum value. Bymagnetic field generated by the high frequency coil 3, the melt 30 b ismoved by convection, and self-stirring occurs. The mass 30 c is melted,and the melt 30 b inside the auxiliary crucible 1 is supplied into themain crucible 11 via the pipe 1 b. Then, the grain-like raw material 20is added into the auxiliary crucible 1 via the feeder 21. Both thecarbon cylinder 2 and the ceramic base 4 are moved downward, and theconductive carbon cylinder 2 covers upper half of the side wall of theauxiliary crucible 1, and the insulating ceramic base 4 is positioned atsuch a height as to cover lower half of the side wall of the auxiliarycrucible 1. Therefore, the melt 30 b in the auxiliary crucible 1 iscontinuously supplied through the pipe 1 a. Because heat is generated onthe carbon cylinder 2, the added grain-like raw material 30 is heated byheat transfer, and melting rate is increased. Also, heat is generated inthe melt 30 b inside the auxiliary crucible 1 due to secondary inductioncurrent. Accordingly, it is possible by this method and by specialarrangement on diameter and shape of the opening of the pipe 1 b, it ispossible to continuously supply the melt 30 b.

Next, detailed description will be given on a third embodiment of anauxiliary melting apparatus of the present invention referring to FIG.8. At the center of the auxiliary crucible 1 made of quartz, a pipe 1 ais formed to supply the melt from the auxiliary crucible 1 to the maincrucible 11 by overflow. The pipe 1 a is arranged in such manner that anopening on the upper end of the pipe 1 a protrudes at a position about ½of the height of the auxiliary crucible 1. The auxiliary crucible 1 issupported by a conductive susceptor 2 (carbon crucible or carboncylinder) so that lateral side and bottom surface are covered, and ahigh frequency coil 3 is disposed around the susceptor 2. Here,secondary induction current is likely to concentrate on the surface of aconductive member, and this tendency becomes more remarkable at higherfrequency. For this reason, thickness of the conductive susceptor 2 andthe frequency applied on the high frequency coil 3 are selected in suchmanner that the thickness of the conductive susceptor 2 will be thinnerthan penetration depth of the secondary induction current.

FIG. 8(a) shows a condition prior to melting, FIG. 8(b) shows acondition during melting process, and FIG. 8(c) shows a condition at thecompletion of melting process. As shown in FIG. 8(a), if high frequencycurrent is applied on the high frequency coil 3 when the raw material 30is till before being melted, i.e. when the initial raw material 30 a isat low temperature and its conductivity is relatively low, secondaryinduction current is generated on the conductive susceptor 2, and Jouleheat is generated on the conductive susceptor 2 by the secondaryinduction current. In this case, conductivity of the initial rawmaterial 30 a is lower than that of high temperature, and secondaryinduction current is not generated almost at all. Therefore, heat of theconductive susceptor 2 is transmitted to the raw material inside via theauxiliary crucible 1. As a result, the raw material is heated, andmelting process is started as shown in FIG. 8(b).

Next, when the raw material is in melting process (30 b in the figure)as shown in FIG. 8(b), conductivity of the raw material is graduallyincreased, and secondary induction current is also generated in the melt30 b. In this case, heat of the conductive susceptor 2 is transmitted tothe raw material inside via the auxiliary crucible 1, and Joule heat isgenerated on the melt 30 b itself by the secondary induction current.Next, as shown in FIG. 8(c), when melting process proceeds andconductivity of the raw material reaches the maximum value and thesecondary induction current in the raw material also reaches the maximumvalue. By magnetic field generated by high frequency coil 3, the melt 30b is moved by convection, and self-stirring occurs. When the rawmaterial 30 is added into the auxiliary crucible 1 via the feeder 21under this condition, the melt 30 b in the auxiliary crucible 1overflows into the pipe 1 a and it is supplied to the main crucible 11through the pipe 1 a.

Next, description will be given on examples of the third embodiment anda conventional example. First, in a conventional example, 1 kg of theraw material Si was heated by resistance heating method, and meltingtime was 75 minutes (35 kWh). Next, in order to melt the same quantityof the raw material in the embodiment:

Coil 3 with inner diameter of 220 mm (10 turns), and

Susceptor 2 with thickness of 10 mm

were used. As a first example of the third embodiment, electric currentof 15 kW with a constant frequency (3 kHz) was applied on the coil 3 atthe starting, and the raw material was melted. Then, AC current of 20 kWwas applied at the additional charging of the material, and melting timewas 30 minutes. Next, in a second example, electric current of 15 kWwith relatively high frequency of 10 kHz was applied on the coil 3 atthe starting as shown in FIG. 8(a). When the raw material is in meltingprocess as shown in FIG. 8(b), electric current of 15 kW with relativelylow frequency of 3 kHz was applied, and the raw material was melted.Then, at the time of additional charging shown in FIG. 8(c), AC currentof 20 kW was applied, and melting time was 20 minutes.

INDUSTRIAL APPLICABILITY

As described above, according to the first invention, when the rawmaterial is at low temperature and its conductivity is relatively low,secondary induction current is generated on the susceptor and heat ofthe susceptor is transmitted to the raw material in the auxiliarycrucible. When the raw material is at high temperature and itsconductivity is relatively high, the susceptor is moved aside andsecondary induction current is generated in the raw material in theauxiliary crucible so the heat is generated in the raw material itself.As a result, it is possible to improve thermal efficiency when the rawmaterial in the auxiliary crucible is heated and melted by inductionheating method, and also to reduce the melting time.

According to the second invention, with the pipe opening blocked by amass of the raw material, the susceptor is arranged at such a positionthat the mass of the raw material is not heated and heating is started.After the melting of the raw material is started, the susceptor isarranged at such a position to heat the mass of the raw material and theraw material above the mass, and heat is generated on both the susceptorand the raw material by secondary induction current. As a result, it ispossible to improve thermal efficiency when the raw material in theauxiliary crucible is heated and melted by induction heating method, andalso to reduce the melting time.

Further, according to the third invention, when the raw material is atlow temperature and its conductivity is relatively low, secondaryinduction current is generated on the susceptor, and heat of thesusceptor is transmitted to the raw material in the auxiliary crucible.When the raw material is at high temperature and its conductivity isrelatively high, secondary induction current is generated in both thesusceptor and the raw material in the auxiliary crucible and heat of thesusceptor is transmitted to the raw material in the auxiliary crucible,and heat is generated in the raw material itself. As a result, it ispossible to improve thermal efficiency when the raw material in theauxiliary crucible is heated and melted by induction heating method, andalso to reduce the melting time. Also, by setting the frequency of thehigh frequency current to be applied to a higher value in the initialstage and by switching over to lower frequency during the process, it ispossible to reduce the melting time further.

What is claimed is:
 1. A single crystal material auxiliary meltingapparatus for heating and melting a single crystal raw material in anauxiliary crucible and for supplying melt into a main crucible, saidapparatus comprising: a conductive susceptor arranged around saidauxiliary crucible so that it can be moved in a vertical direction; acoil wound around said susceptor and with high frequency current appliedthereon; and means for moving said susceptor in such manner that heatingof the raw material in said auxiliary crucible is started by arrangingsaid susceptor at a high position on said auxiliary crucible and byheating said susceptor with secondary induction current, said susceptoris moved aside from said position on said auxiliary crucible aftermelting of said raw material has been started, and the raw material insaid auxiliary crucible is heated by secondary induction current.
 2. Thesingle crystal material auxiliary melting apparatus according to claim1, wherein there is provided means for moving the susceptor, an openingof a pipe for supplying melt from said auxiliary crucible into said maincrucible by overflow is protruded by a height from a bottom surface ofsaid auxiliary crucible, and when new raw material is added into saidauxiliary crucible after said raw material has been melted, saidsusceptor is moved so that the height of the lower end of said susceptoris approximately aligned with the height of said pipe opening.
 3. Thesingle crystal material auxiliary melting apparatus according to claim2, wherein thickness of said susceptor and frequency applied on saidcoil are selected in such manner that the thickness of said susceptorwill be thinner than penetration depth of the secondary inductioncurrent, said penetration depth being determined by the frequency. 4.The single crystal material auxiliary melting apparatus according toclaim 1, wherein thickness of said susceptor and the frequency of thecurrent applied on said coil are selected in such manner that thethickness of said susceptor will be thinner than penetration depth ofthe secondary induction current, said penetration depth being determinedby the frequency.
 5. A single crystal material auxiliary meltingapparatus for heating and melting a single crystal raw material in anauxiliary crucible and for supplying melt into a main crucible, saidapparatus comprising: a conductive susceptor arranged around saidauxiliary crucible so that it can be moved in a vertical direction; acoil wound around said susceptor and with high frequency current appliedthereon; and a pipe having an opening to supply the melt from saidauxiliary crucible into said main crucible and formed on the bottom wallof said auxiliary crucible, whereby: means for starting to heat the rawmaterial in said auxiliary crucible by generating heat on said susceptorwith secondary induction current and by arranging said susceptor at sucha height that a mass of said raw material is not heated and the rawmaterial above the mass is heated, and the mass of the raw materialblocks the opening of said pipe; and means for generating heat on boththe susceptor and the raw material with secondary induction current andby arranging said susceptor at such a height that the mass of said rawmaterial and the raw material above the mass are heated after melting ofsaid raw material has been started.
 6. A single crystal material meltingmethod in a single crystal material auxiliary melting apparatus, whichcomprises an auxiliary crucible for heating and melting a single crystalraw material and for supplying melt into a main crucible, a conductivesusceptor arranged around said auxiliary crucible so that said susceptorcan be moved in a vertical direction, and a coil wound around saidsusceptor and with high frequency current applied thereon, whereby saidmethod comprises the steps of: starting to heat the raw material in saidauxiliary crucible by arranging said susceptor at a high position onsaid auxiliary crucible and by generating heat on said susceptor withsecondary induction current; and moving said susceptor aside from thehigh position on of the auxiliary crucible after melting of said rawmaterial has been started, and generating heat on the raw material insaid auxiliary crucible by secondary induction current.
 7. The singlecrystal material melting method according to claim 6, said method beingused in a single crystal material auxiliary melting apparatus, whichcomprises an opening of a pipe for supplying the melt from saidauxiliary crucible into said main crucible by overflow and beingprotruded by a height from bottom surface of said auxiliary crucible,said method comprises the steps of: adding new raw material into saidauxiliary crucible after said raw material has been melted; andarranging in such manner that the position of the lower end of saidsusceptor is approximately aligned with the position of said pipeopening.
 8. The single crystal material melting method according toclaim 7, wherein thickness of said susceptor frequency applied on saidcoil are selected in such manner that the thickness of said susceptorwill be thinner than penetration depth of the secondary inductioncurrent, said penetration depth being determined by the frequency. 9.The single crystal material melting method according to claim 6, whereinthickness of said susceptor and frequency applied on said coil areselected in such manner that the thickness of said susceptor will bethinner than penetration depth of the secondary induction current, saidpenetration depth being determined by the frequency.
 10. A singlecrystal material auxiliary melting apparatus for heating and melting asingle crystal raw material in an auxiliary crucible and for supplyingmelt into a main crucible, said apparatus comprising: a conductivesusceptor for supporting said auxiliary crucible; and a coil woundaround said susceptor and with high frequency current applied thereon,whereby: heating in the auxiliary crucible is started by applyingelectric current with relatively high first frequency on said coil andelectric current with relative low second frequency is applied aftermelting of said raw material has been started.
 11. The single crystalmaterial auxiliary melting apparatus according to claim 10, wherein thethickness of said susceptor and said second frequency applied on saidcoil are selected in such manner that the thickness of said susceptorwill be thinner than penetration depth of the secondary inductioncurrent, said penetration depth being determined by the frequency.
 12. Asingle crystal material melting method in a single crystal materialauxiliary melting apparatus for heating and melting a single crystal rawmaterial in an auxiliary crucible and for supplying melt into a maincrucible, said apparatus comprising: a conductive susceptor forsupporting said auxiliary crucible; and a coil wound around saidsusceptor and with high frequency current applied thereon, said methodcomprises the steps of: applying electric current with relatively highfirst frequency on said coil and starting to heat the material in saidauxiliary crucible; and applying electric current of relatively lowsecond frequency after melting of said raw material has been started.13. The single crystal material melting method according to claim 12,wherein thickness of said susceptor and said second frequency applied onsaid coil are selected in such manner that the thickness of saidsusceptor will be thinner than penetration depth of the second inductioncurrent, said penetration depth being determined by the frequency.
 14. Asingle crystal material melting method in a single crystal materialauxiliary melting apparatus, which comprises an auxiliary crucible forheating and melting a single crystal raw material and for supplying meltinto a main crucible, a conductive susceptor arranged around saidauxiliary crucible in such manner that said susceptor can be moved in avertical direction, a coil wound around said susceptor and with highfrequency current applied thereon, and a pipe with an opening forsupplying the melt from said auxiliary crucible into said main crucible,said pipe being formed on a bottom wall of said auxiliary crucible,whereby said method comprises the steps of: arranging said susceptor atsuch a position so that said susceptor covers a range of side wall ofsaid auxiliary crucible starting from an upper end of said auxiliarycrucible and so as not to heat said raw material mass but to heat theraw material above said mass with the raw material mass placed on theopening of said pipe, and starting to heat the raw material in saidauxiliary crucible by generating heat on said susceptor due to thesecondary induction current; and arranging said susceptor at such aheight as to heat said raw material mass and the raw material above saidmass after melting of said raw material has been started, and generatingheat on both of said susceptor and said raw material due to secondaryinduction current.
 15. A single crystal material auxiliary meltingapparatus for heating and melting a single crystal raw material in anauxiliary crucible and for supplying melt into a main crucible, saidapparatus comprising: a conductive susceptor for supporting saidauxiliary crucible; and a coil wound around said susceptor and with highfrequency current applied thereon, whereby: thickness of said susceptorand frequency applied on said coil are selected in such manner than thethickness of said susceptor will be thinner than penetration depth ofthe secondary induction current.